Any person who is at least twenty-one years of age and who is not himself a drug dependent person who violates this act by distributing a controlled substance listed in schedules I through V to a person under eighteen years of age who is at least four years his junior is punishable by a term of imprisonment up to twice that otherwise authorized by subsection (f) of section 13 of this act, in addition to any fine authorized by this act.
35 P.S. § 780-114